KR20080080802A - Apparatus and method to combat inter-antenna interference in a orthogonal frequency divisiong multiplexing access system - Google Patents

Abstract

An apparatus and a method for assigning sub-channels to suppress inter-antenna interference in an OFDMA(Orthogonal Frequency Division Multiplexing Access) system are provided to support high data rate by transmitting high capacity data and video through broadband modulation. A method for assigning sub-channels to suppress inter-antenna interference in an OFDMA system includes the steps of: selecting and connecting communicable distributed antennas satisfying a data transmission rate required in a mobile terminal(412); re-queuing the distributed antenna with maximal transmission power first in the same cell(414); and assigning sub-channels to the distributed antennas from the distributed antenna with the top priority(424).

Description

Apparatus and method for allocating subchannels for inter-antenna interference suppression in orthogonal frequency division multiple access systems

The present invention relates to an apparatus and method for subchannel allocation in an Orthogonal Frequency Division Multiplexing Access (hereinafter referred to as "OFDMA"). In particular, the present invention relates to orthogonal frequency division that minimizes interference between antennas while satisfying a user-required transmission rate. A subchannel allocation apparatus and method for inter-antenna interference suppression in a multiple access system.

Due to the development of the communication industry and increasing user demand for Internet services, the necessity for a communication system capable of efficiently providing Internet services is increasing. Existing communication networks have been developed mainly for voice services, which have relatively small data transmission bandwidths and high usage fees.

In addition, as a representative example of a broadband wireless access method for solving such a disadvantage, research on the OFDM method is rapidly progressing.

The OFDM scheme is a typical transmission scheme using a multi-carrier, which converts a serially input symbol string in parallel and modulates the converted symbol string through a plurality of sub-carriers having mutual orthogonality. That's the way it is. The OFDM scheme can be widely applied to a digital transmission technology that requires high-speed data transmission such as wireless Internet, digital audio broadcasting (DAB), digital television, and wireless local area network (WLAN).

The orthogonal frequency division multiplexing (OFDM) (see references [3] and [4]) is a multiplexing technique for subdividing a bandwidth into multiple frequency subcarriers.

In OFDM, the input data stream is divided into several parallel substreams having a reduced data rate (and thus increasing symbol length), each substream being transmitted on a modulated and separated orthogonal subcarrier. Increasing the symbol length improves the robustness of OFDM to delay spread. OFDM modulation can be realized with an efficient inverse fast Fourier transform (IFFT), which allows for multiple subcarriers with low complexity.

In the OFDM system, channel resources are allowed using OFDM symbols in the time domain and subcarriers in the frequency domain. Time and frequency resources are organized into subchannels for allocation to individual users.

The Orthogonal Frequency Division Multiplexing (OFDM) scheme provides multiplexing operations for data streams from multiple users to uplink (UL) multiple access using downlink (DL) subchannels and uplink subchannels. -Access / multiplex method.

As mentioned above, the subcarriers are usually grouped into subsets called sub-channels. For example, in a WiMAX system, an OFDMA symbol structure consists of three types of subcarriers: data subcarriers for data transmission, pilot subcarriers for evaluation and synchronization, and null subcarriers for guard bands and DC carriers. Active (data and pilot) subcarriers are all grouped into subchannels.

The WiMAX OFDMA physical layer (see references [5] and [6]) supports sub-channelization in both downlink (DL) and uplink (UL), and the minimum frequency of sub-channelization The time resource unit is one slot.

Therefore, research on adaptive subcarrier (subchannel) allocation algorithm in a multi-user OFDMA system has been extensively performed. However, most of these algorithms are based on centralized antenna systems (CAS).

In a distributed antenna system (DAS) based on the OFDMA, subcarriers may be used by other antennas.

In general, Distributed Antenna Systems (DAS) (see references [1], [2]) can provide macro-diversity by suppressing massive fading and reducing access distance by geometrically distributing the antenna. . This was first introduced to solve the coverage (receivable area) problem for indoor wireless systems and later to improve the performance of CDMA systems.

FIG. 1 illustrates a coverage area for each distributed antenna distributed around a base station in a distributed antenna system. Referring to FIG. 1, in a distributed antenna system, BS antennas are geometrically uniformly distributed, and each BS antenna is placed at the center of a hexagonal region, and then the entire region is divided into several hexagonal sub-areas. It can be divided into When the average access distance in the distributed antenna system is reduced, the transmission power is reduced, so that interference can be reduced and capacity can be expanded. In each frame, the channel conditions of these BS antennas are measured and analyzed by the subscriber station (SS), and the antenna M with the highest channel gain can be selected as the serving antenna in the next frame. The M value can be 1 or greater. In this case, M is limited to 1 to have a positive value.

If the number of antennas is P in one cell of the distributed antenna system, the deployed subcarriers are P times larger than that of the centralized antenna system (CAS). Thus, resource allocation in distributed antenna systems is more complicated.

Currently, a distributed antenna system based on OFDMA can be classified into several types of subchannel allocation algorithms as follows.

1. Each antenna deploys all subchannels.

2. All subchannels are assigned only once to a cell. This means that if a subchannel was used by one antenna in a cell, it could not be used by any other antenna in the same cell.

3. Subchannels are allocated from a global point of view, and two user antennas are allowed to use the same subchannel in one user mobile terminal to obtain diversity gain.

However, if each antenna deploys all subchannels as described above, this is the same as cell division in terms of frequency reuse, which will result in severe inter-antenna interference similar to co-channel interference in cell division, and also all subchannels. If a channel is deployed on only one remote antenna and one subscriber mobile terminal, even if it excludes interference to other antennas, this is a waste of bandwidth, especially in hot zones.

Therefore, in a distributed antenna system based on the current OFDMA, subchannels cannot be reused even if two antennas are sufficiently far from each other.

As such, if each antenna deploys all subchannels, this is the same as cell partitioning in terms of frequency reuse, which causes a problem that results in severe antenna-to-antenna interference similar to common channel interference in cell partitioning.

An object of the present invention for solving the above problems relates to an apparatus and method for allocating subchannels in OFDMA. In particular, different subchannels are provided to adjacent antennas in order to satisfy user request rate and to minimize inter-antenna interference. An apparatus and method for allocating subchannels for inter-antenna interference suppression in an orthogonal frequency division multiple access system for allocating a DMA.

According to an aspect of the present invention to achieve the above object, in the distributed wireless communication system having a distributed antenna that is geographically randomly distributed and can communicate with multiple mobile terminals at the same time, In the channel allocation method, a process of selecting and accessing a distributed antenna that satisfies the data rate required by the mobile terminal and communicating with each other, and a distributed antenna having the maximum transmission power in the same cell as the highest priority (Re-) queue) and allocating subchannels sequentially from the corresponding distributed antenna of the highest priority.

According to another aspect of the present invention to achieve the above object, in a base station apparatus for allocating a subchannel for inter-antenna interference suppression in a distributed wireless communication system, the antenna adjacent to the antenna to which the subchannel is assigned And a first allocator for searching for subchannels, and a second allocator for allocating subchannels sequentially from the distributed antennas by setting the highest priority of the distributed antennas.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, specific details such as specific components are shown, which are provided to help a more general understanding of the present invention, and the specific details may be changed or changed within the scope of the present invention. It is self-evident to those of ordinary knowledge in Esau.

2 is a block diagram illustrating the concept of a subchannel allocation scheme for avoiding adjacent antennas using the same subchannel in an orthogonal frequency division multiple access system according to an embodiment of the present invention.

Referring to FIG. 2, if subchannel A is used by antenna 1 serving one subscriber station SS in its coverage area, adjacent antennas 2, 6, and 7 are subchannel A used by antenna 1. Avoid the use of. The antennas 2, 6, and 7 use the remaining subchannels other than the subchannel A used by the antenna 1. Here, since antenna 4 is not adjacent to antenna 1, subchannel A can be used, and interference with antenna 1 is hardly caused.

According to the above-described configuration, the present invention avoids inter-antenna interference due to allocation of the same subchannel while satisfying the service requirement of the user mobile terminal, and utilizes all channel resources up to the maximum.

3 is a block diagram showing a part of the overall internal configuration of a base station to which subchannel allocation is performed in downlink of the OFDMA system according to the present invention. The subchannel allocation apparatus according to the present invention is particularly implemented through the subchannel allocation apparatus 30 provided in the base station.

The signal transmitted from the base station of FIG. 3 passes through a frequency selective fading channel unique to each mobile terminal corresponding to K subscribers, and is then received by the mobile terminal of each subscriber. Referring to FIG. 3, the subchannel allocation apparatus 30 receives user request rates transmitted from mobile stations of all subscribers and subchannel allocation information previously allocated to each of the subscriber mobile terminals at preset allocation periods. The subchannel allocation apparatus 30 sequentially adapts the allocation scheme according to the present invention for each allocation period by using the inputted request rate for each subscriber, and then adapts the subchannel allocation unit 31, 32, and 33 in the first and second allocation units 31, 32, and 33. Perform channel assignments and bits.

On the other hand, although not shown in Figure 3, the base station receives the user request rate and sub-channel allocation information transmitted from the mobile terminal of each subscriber for input to the first, second, third allocation unit (31, 32, 33) A receiver may be provided, which may use a known technique, and thus a detailed description thereof will be omitted.

In addition, in the present invention, it is assumed that non-real time data having a subscriber request rate of zero or a positive value and subscriber data divided into real time data having a positive request rate of a positive value are transmitted in the same cell.

A detailed description of the allocation method according to the present invention will be described with reference to FIG.

First, to explain the basic conditions that the present invention presupposes to aid the understanding of the present invention, it is assumed that there are P antennas, N subchannels, and K users in the entire cell, and the minimum data rate required for each SS is The channel quality from the antenna p to the user mobile terminal SS k for the subchannel n is represented by a bit. Represented by For example, if Quadrature Phase Shift Keying (QPSK) coding with R = 2/3 is used, Bit.

The lowercase letter k is a variable for distinguishing a user, and N is the total number of subchannels. And C Is the number of bits per symbol allocated to the nth subchannel of the k-th user, and the number of bits per symbol C Is a positive real number, for example. It is possible to allocate a positive real number rather than a positive integer in bits per symbol through a combination of modulation and error control codes.

And symbol d means an adjacent antenna. For example, if antenna p is adjacent to antenna q, Is set to, otherwise to be.

The first, second, third and fourth step allocation algorithms according to an embodiment of the present invention are expressed as follows.

<Step 1 Allocation Algorithm>

,

For ( )

{Calculate ， -<Equation 1>

Select -<Equation 2>

( End} is the set of all users served by antenna p)

<Step 2 Allocation Algorithm>

For ( )

{

Calculate -<Equation 3>

end}

If you re-queue P according to Which Greater than

<Three-stage Allocation Algorithm>

, ,

(Initially all subchannels are available.

Is a set of subchannels assigned to antenna p,

Is a set of subchannels used by adjacent antennas of p)

For ( )

{

for

if then

end}

(Search all subchannels already in use by adjacent antennas)

For

while

Select -<Equation 4>

(Subchannel Is assigned to antenna p and user k)

<4 step allocation algorithm>

For ( )

if and to this k, then

while

select

(Subchannel This is assigned to antenna p and user k.)

4 is a flowchart illustrating a subchannel allocation method for inter-antenna interference suppression in an orthogonal frequency division multiple access system according to an embodiment of the present invention. Referring to FIG. 4, in step 410, the base station receives a subscriber request rate transmitted from mobile stations of all subscribers at a predetermined allocation period. Data rate C required by subscriber mobile station served by any antenna p Is calculated using Equation 1 above.

The highest C for the antenna selected using Equation 2 above Select the best P with (step 412).

A plurality of distributed antennas are liquefied using Equation 3 with the antenna p selected in step 412 as the highest priority (step 414).

In step 416, the subchannels to be allocated are sequentially selected from the corresponding distributed antenna of the highest priority. In this case, a subchannel used by another distributed antenna adjacent to the corresponding distributed antenna neighboring area is searched (step 418). Here, the number of adjacent dispersing antennas is at least one.

In operation 420, the selected subchannel and the subchannel used by the adjacent distributed antenna are compared using Equation 4.

If the same subchannel as the subchannel to be allocated to the corresponding distributed antenna is found in step 420, that is, if a subchannel selected by another adjacent antenna is already used, the process returns to step 416 to use the remaining channel. Steps 418, 420, and 422 are performed again. If the same subchannel is not found in step 420, the subchannel is allocated to the corresponding distributed antenna (step 422).

As described above, the configuration and operation of an apparatus and method for allocating subchannels for inter-antenna interference suppression in an orthogonal frequency division multiple access system according to an embodiment of the present invention can be performed. Although examples have been described, various modifications can be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be defined by the described embodiments, but by the claims and equivalents of the claims.

References

[1] A. M. Adel, A. Saleh, A. J. Rustako and R. S. Roman, "Distributed antennas for indoor radio communications," IEEE Trans. Commun, vol. 35, pp. 1245-1251, Dec., 1987.

[2] S. Zhou, M. Xhao, X. Xu, J. Wang, and Y. Yao, and Y. Yao, “Distributed wireless communications system: a new architecture for future public wireless access,” IEEE Commun. Mag., Vol. 17, no. 3, pp. 108-113, March 2003.

[3] L.J. Cimini, "Analysis and Simulation of a Digital Mobile Channel Using Orthogonal Frequency Division Multiplexing," IEEE Trans. Comm., Vol. COM-33, no. 7, pp665-675, June 1985.

[4] Richard Van Nee and Ramjee Prasad, "OFDM for wireless Multimedia Communications," Artech House, 2000.

[5] Revision of IEEE Std 802.16-2001, "IEEE standard for local and metropolitan area networks-Part 16: Air interface for fixed broadband wireless access systems," Oct. 2004.

[6] IEEE 802.16e -2005, "IEEE standard for local and metropolitan area networks-Part 16: Air interface for fixed and mobile broadband wireless access systems," Feb. 2006.

As described above, according to the present invention, by minimizing the interference between antennas by avoiding the same subchannels between adjacent antennas when allocating subchannels, larger system capacity can be obtained because the interference of the cells is not affected, and large data can be obtained. And because the video can be transmitted through a wideband modulation method, it has a very flexible feature and high data rate in terms of bandwidth requirements.

1 illustrates a coverage area for each distributed antenna distributed around a base station in a general distributed antenna system;

2 is a block diagram illustrating a concept of a subchannel allocation method for avoiding adjacent antennas using the same subchannel in an orthogonal frequency division multiple access system according to an embodiment of the present invention.

3 is a block diagram illustrating a part of the overall internal configuration of a base station to which subchannel allocation is performed in downlink of an orthogonal frequency division multiple access system according to the present invention;

4 is a flowchart illustrating a subchannel allocation method for inter-antenna interference suppression in an orthogonal frequency division multiple access system according to an embodiment of the present invention.

Claims (7)

A sub-channel allocation method for inter-antenna interference suppression in a distributed wireless communication system having a randomly distributed geographically distributed antenna capable of communicating with multiple mobile terminals simultaneously, Selecting and accessing a distributed antenna that satisfies the data rate required by the mobile terminal and is capable of communicating; Re-queue the highest priority of the distributed antenna in the same cell; And allocating subchannels sequentially from the corresponding distributed antennas of the highest priority.  The method of claim 1, wherein when assigning the subchannels, Searching for a subchannel used by a distributed antenna located in a neighboring area around the corresponding distributed antenna; And allocating the remaining subchannels except the searched subchannels. The method of claim 1, further comprising: searching and assigning a subchannel not used in the corresponding distributed antenna connected to the mobile terminal when the data rate required by the mobile terminal is not satisfied. Subchannel Allocation Method for Inter-antenna Interference Suppression in Frequency Division Multiple Access Systems. 2. The method of claim 1, wherein the distributed antenna further includes feeding back information of the available subchannels to a base station. A base station apparatus for allocating subchannels for inter-antenna interference suppression in a distributed wireless communication system, A first allocator for searching a subchannel used by an antenna adjacent to a corresponding antenna to which the subchannel is allocated; A subchannel for interference suppression between antennas in an orthogonal frequency division multiple access system, comprising a second allocator configured to assign a sub-antenna having a maximum transmission power as a highest priority and sequentially assign subchannels from the distributed antenna. Allocation unit. The method of claim 5, wherein the base station, Orthogonal frequency division multiple access system further comprising: a third allocation unit for searching and allocating subchannels not used in the corresponding distributed antenna connected to the mobile terminal when the data rate required by the mobile terminal is not satisfied. Subchannel Allocation for Inter-antenna Interference Suppression The method of claim 5, wherein the base station, A subchannel allocation apparatus for inter-antenna interference suppression in an orthogonal frequency division multiple access system, wherein the subchannel allocation allocates a subchannel that is not the same as a distributed antenna of a region adjacent to the corresponding distributed antenna.